/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

package org.apache.iotdb.confignode.procedure.scheduler;

import org.apache.iotdb.confignode.procedure.Procedure;

import java.util.concurrent.TimeUnit;

/**
 * Keep track of the runnable procedures
 */
public interface ProcedureScheduler {
    /**
     * Start the scheduler
     */
    void start();

    /**
     * Stop the scheduler
     */
    void stop();

    /**
     * In case the class is blocking on poll() waiting for items to be added, this method should awake
     * poll() and poll() should return.
     */
    void signalAll();

    /**
     * Inserts the specified element at the front of this queue.
     *
     * @param proc the Procedure to add
     */
    void addFront(Procedure proc);

    /**
     * Inserts the specified element at the front of this queue.
     *
     * @param proc   the Procedure to add
     * @param notify whether need to notify worker
     */
    void addFront(Procedure proc, boolean notify);

    /**
     * Inserts the specified element at the end of this queue.
     *
     * @param proc the Procedure to add
     */
    void addBack(Procedure proc);

    /**
     * Inserts the specified element at the end of this queue.
     *
     * @param proc   the Procedure to add
     * @param notify whether need to notify worker
     */
    void addBack(Procedure proc, boolean notify);

    /**
     * The procedure can't run at the moment. add it back to the queue, giving priority to someone
     * else.
     *
     * @param proc the Procedure to add back to the list
     */
    void yield(Procedure proc);

    /**
     * @return true if there are procedures available to process, otherwise false.
     */
    boolean hasRunnables();

    /**
     * Fetch one Procedure from the queue
     *
     * @return the Procedure to execute, or null if nothing present.
     */
    Procedure poll();

    /**
     * Fetch one Procedure from the queue
     *
     * @param timeout how long to wait before giving up, in units of unit
     * @param unit    a TimeUnit determining how to interpret the timeout parameter
     * @return the Procedure to execute, or null if nothing present.
     */
    Procedure poll(long timeout, TimeUnit unit);

    /**
     * Returns the number of elements in this queue.
     *
     * @return the number of elements in this queue.
     */
    int size();

    /**
     * Clear current state of scheduler such that it is equivalent to newly created scheduler. Used
     * for testing failure and recovery.
     */
    void clear();
}
